The present invention relates to a lamp drive device of a projector such as a liquid crystal projector or the like.
With a prior art projector, a high voltage is applied between two electrodes of a lamp (for example a mercury lamp) and an arc is generated. Due to generation of this arc, a lamp drive current flows through the lamp, and this causes light to be emitted. However, since with such a lamp for a projector the gap between the electrodes is narrow, accordingly very occasionally, after the current is cut off, the mercury causes a short circuit (a bridge short). On the other hand, generally, in order to keep the output of the lamp constant, constant power control is performed at its rated output. Accordingly sometimes, even though the mercury has caused a bridge short, the power continues to flow while the constant power continues to be maintained. In this type of case, there is a possibility that this will lead to the fault that the lamp drive circuit gets into an overheated state.
In order to solve the problem described above, in Japanese Laid-Open Patent Publication Heisei 8-273865, there is proposed a lamp drive circuit which reliably turns the lamp supply voltage OFF when the lamp has become incapable of lighting up. According to this circuit, it is possible to prevent the drive circuit being damaged due to the lamp supply voltage.
However, this lamp drive circuit disclosed in Japanese Laid-Open Patent Publication Heisei 8-273865 described above is not capable of solving the shorting problem between the electrodes due to bridge shorting by the mercury within the lamp and the like.
The objective of the present invention is to provide a lamp drive device of a projector which controls the projector lamp by constant power control, and which is capable of reliably deciding that the electrodes within the lamp have shorted out, thereby being able to protect the circuit.